I. Field
The following description relates generally to communication systems, and more particularly, to a method and apparatus for determining the spatial channels in a Spatial Division Multiple Access (SDMA)-based wireless communication system.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple In, Multiple Out (MIMO) technology represents one such approach that has recently emerged as a popular technique for next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface (air link medium) standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
In wireless communication systems, Medium Access Control (MAC) protocols are designed to exploit several degrees of freedom offered by the air link medium. The most commonly exploited degrees of freedom are time and frequency. For example, in the IEEE 802.11 MAC protocol, the time degree of freedom is exploited through the Carrier Sense Multiple Access (CSMA) protocol. The CSMA protocol attempts to ensure that no more than one transmission occurs in a neighborhood of potential high interference. The frequency degree of freedom can be exploited by using different channels.
Recent developments have led to the space dimension being a viable option. SDMA can be used for improving utilization of the air link medium by scheduling multiple terminals for simultaneous transmission and reception. Data is sent to each of the terminals using spatial streams. For example, with SDMA, a transmitter forms streams of transmissions (“transmission streams”) that are orthogonal to individual receivers. Such orthogonal streams can be formed because the transmitter has several antennas and the transmit/receive channel consists of several paths. The receivers may also have one or more antennas such as in Single In, Multiple Out (SIMO) or MIMO receivers. For this example, assume that the transmitter is an access point (AP) and the receivers are stations (STAs). The streams are formed such that a stream targeted at a Station 1 (STA-1), for example, is seen as low power interference at a Station 2 (STA-2), and a Station 3 (STA-3). In order to form the orthogonal streams, the AP needs to have the Channel State Information (CSI) from each of the receiving STAs. The CSI can be measured and communicated in several ways. Disclosed are aspects that describe efficient requesting, gathering, and computing of the channel state information of the spatial streams. The various described aspects may be useful for Very High Throughput (VHT) transmissions in a wireless network.
Consequently, it would be desirable to address one or more of the deficiencies described above.